Rotary coin mechanisms are widely used in merchandise-dispensing machines such as bulk vendors for dispensing gumballs and other small articles. An example of such a coin mechanism is described and illustrated in U.S. Pat. No. 5,383,545 issued Jan. 24, 1995 to Schwarzli, which is incorporated herein by reference.
Bulk vendors are designed for self service by users with minimal maintenance, and as such are frequently placed in locations where their use cannot be readily supervised. As a result bulk vendors are constantly subjected to attempts to steal merchandise, usually by children and adolescents.
By far the most common type of theft from bulk vendors involves the use of "slugs" approximating the size of the coins which the coin mechanism is designed to accept. This has led to the development of measuring devices with fairly precise tolerances, capable of determining the thickness and diameter of the inserted coin to within a few thousandths of an inch. However, while in the past slugs were commonly cut or stamped out of sheet metal metal, more recently slugs composed of plastic or sturdy cardboard have become popular due to their low cost and the ease with which such slugs can be produced to the required size.
Cardboard slugs present a particular problem in bulk vendors, because of the manner in which a conventional rotary coin mechanism discriminates between coins of the intended denomination and other coins or slugs. A coin recess is provided in a rotating coin conveyor disc, and a pair of dogs respectively measure the thickness and diameter of the inserted coin or slug. Either dog will arrest rotation of the mechanism if the diameter or thickness does not match that of the intended denomination of coin. However, in the case of slightly oversized cardboard slugs of the correct thickness, repeated attempts to force the mechanism to turn with the slug in the coin recess actually result in gradual wearing away of the edge of the slug, and once the edge has worn to a size within the tolerance of the measuring dog the mechanism will accept the slug. This has become a significant problem resulting in extensive losses to bulk vendor operators.